Apparatus for melting glass and the like



Sept. 20, 1955 G. HENRY ET AL APPAfiATU-S FOR MELTING GLASS AND THE LIKEOriginal Filed July 17, 1947 INVENTo s A TT'OR Y United States Patent '0APPARATUS FOR MELTING GLASS AND THE LIKE Georges Henry, Dampremy, andEdgard Brichard, Jurnet- Houbois, Belgium, assignors of one-third toUnion des Verreries Mecaniques Belges, Charleroi, Belgium, a Belgiancompany Original application July 17, 1947, Serial No. 761,632,

now Patent No. 2,634,555, dated April 14, 1953. Dividedsalnd thisapplication October 31, 1952, Serial No. 320,5

4 Claims. (Cl. 49-64} The present invention relates to an apparatus forthe manufacture of glass and like products and it has for its object toimprove the thermal efliciency of the fusion of these materials. As likeproducts are to be understood herein, enamels, silicates, basalts andgenerally products which at high temperature give rise to the Lphenomenon of so-called pasty fusion. This application is a division ofour copending application, Serial No. 761,632, filed July 17, 1947 (nowU. S. Patent 2,634,555, dated April 14, 1953).

An object of the invention is to provide a furnace or oven for carryingout the process described and claimed in our said Patent No. 2,634,555,in which the heat necessary for melting the raw materials and heatingthem to the required temperature is supplied by blowing flames underhigh pressure and at a high rate of flow through the bath.

In ovens at present used in the manufacture of glass, the heating gasescirculate under a pressure very near atmospheric, dilfering from thelatter only by a few millimeters more or less of water column. The rateof flow, calculated at normal pressure and temperature, is normally ofabout 3 meters per second; it can exceptionally reach 8 m./s. Higherrates of flow can be adopted without inconvenience, as if the flame isintroduced under high pressure and at high speed into a free enclosure,it

heats the walls to such high temperature that it brings about a speedydestruction thereof.

It follows that in the usual melting ovens, the cross sectional area ofthe inlet and outlet flues must be very large in order to provide thenecessary delivery. The heat exchange surfaces, both in the oven itselfand in the apparatus for recuperating waste heat, must alsobe veryextensive in view of the low transmission coeflicients corresponding tooperating conditions. Moreover the volume and the weight of the mainapparatus and of the r accessories to the oven, and the surfaces exposedto external losses are very great.

It results therefrom that the thermal efl'iciency of the fusion is verylow, namely of the order of 20%. This type of apparatus is diflicult tooperate on account of its size and the large masses which are involved.Its construction and upkeep is costly.

It has been proposed to melt glass by blowing air and gas into the mass,but processes of this kind have not been developed, as with the usualflow rates and pressures on ordinary furnaces, results are mediocre. Itis seen that under these conditions the flame overheats the walls nearthe blowing nozzles and causes their speedy destruction at the same timeas the destruction of the nozzles themselves. Heat losses are importantand the operation of the blowers is unsatisfactory: the melted masstends to surge back towards the orifices which ,it partly obstructsbefore it is again violently projected outwards, the combustion thusbeing irregular.

The apparatus according to the present invention comprises a shaftcommunicating at its bottom with a melting pot, the shaft having aconstriction above the melting "ice pot, air and gas nozzles openinginto the bottom of the pot for supplying air and gas thereto, means atthe top of the shaft for supplying powdered raw materials and fordelivering these materials spray-fashion over the entire cross-sectionalarea of the shaft, and an outlet above the delivering means forevacuating the burned gases from the shaft.

In operating the apparatus the fuel and air previously raised to apressure that is at least of 2000 mm. of water column i. e. about aboveatmospheric pressure and may reach several atmospheres, are blowndirectly into the molten mass at a rate that is at least of meters persecond (at normal temperature and pressure) and may reach severalhundreds of meters per second. Under these conditions the flux of heatis well concentrated into a reduced zone whereby apparatus of small sizemay be used. Under influence of high pressure and high rate of speed,the heat transmission coeflicients are considerably increased.

This effect is marked in the melting oven itself as well as in the heatrecuperation apparatus wherein, with this process, it is possible tocirculate, at high pressure and high rate of speed, both the burnt gasesand the gases to be preheated.

In this apparatus, the drawbacks which were due to the lack ofuniformity of combustion and to the destruction of the walls no longerexist. It is found, in fact, that when gases are blown at a rate ofspeed above 30 meters per second into a mass of molten glass, themaximum temperature no longer builds up in proximity to the nozzles, butat a certain distance of the point of injection, that is well within themolten mass. The nozzles and the adjacent walls are thus protectedagainst overheating and an excellent use of the available heat isobtained, the flame being completely surrounded with molten productswhich offer thereto the largest possible exchange surface.

Furthermore, owing to the high speed of the flames, the molten mass isbrought to a state of extreme turbulence. The surfaces ofiiered to theaction of the flames are continuously renewed, whereby the heattransmission a is still materially improved. The stirring of the bath isalso favorable to the homogeneity of the finished product.

The pressure of the gases also results in increasing the rate ofcombustion so that the combustion can be quickly completed and the fumescan yield to the bath f the whole of their useful sensible heat beforethey escape; this being all the more so since, by reason of the highrate of combustion, the temperature of the flame is very high and nearthe theoretical combustion temperature.

On the other hand the fusion under high pressure is of such nature as togive rise, by expansion of the gases contained in the glass, to anincrease in the number and the size of occluded bubbles. It is knownthat the presence of a large number of big bubbles travelling throughthe bath is favorable to the refining of the glass. The result is bubblyglass which may be used as such for some special purposes, or may berefined in a separate oven or in a rest zone suitably provided in themelting furnace itself.

The pressure and rate of speed of the flames, combined with the efficacyof the heat transmission in the turbulent mass make it possible todevelop within a restricted space a very large quantity of heat. Incomparison with the usual construction, the heat transmission per squaremeter of free surface of the bath is raised from kgcaL/mF/sec. to morethan 600 kgcaL/mF/sec. Consequently the size of the apparatus may bereduced in a proportion of about 1 to 10, the heat losses through thewalls thus becoming very low.

In operating the apparatus the chemical nature and the physical aspectof the finishing product may be modified by 'g'ivingto'the injectedmixture a determined chemical composition. For example 'in glassescontaining bodies which, according to their degree of oxidation, modifythe color of the glass, the coloring may be varied by usinga more orless oxiding or a more or less reducing flame. I Thus, in the case ofiron-containing glass, if the ratio of gas delivery to-air delivery isincreased, a reducing flame is obtained which'willmodify the colortowards blue, whereas if the gas/air ratio is decreased, an oxidizingflame is ohtained that will give the glass a lighter greenish hue.We-may also add to the comburentor'to the fuel, reagents such, forinstance, as gaseous coloring substances or colored-substances dispersedas a fine dust so that they may be held in suspension in the fuelor inthe -comburent. V

For example with the use of non-desulturized cokeoven gas'as fuel, theoperationcarried out in reducing atmosphere will give glass of yellowcolor due to sulfides.

The fumes escaping fromthe bath may advantageously be kept underrelatively high pressure and may travel at high speed in order topromote the heat exchange with the fresh raw material and/or'with thefuel and the combustion air, or for recuperating their heat for anyother purpose. By causing the'fumes to expand in a suitable mechanicaldevice all or part of the energy used in compressing the heating gasesmay be recovered.

In order to preheat the raw materials in a divided state, it isadvantageous to drop these spray-fashion onto the molten mass, so thatthey fall in contra-current through the ascending combustion gasesissuing from the mass.

Into the layer or mass of molten glass in the melting pot are blown theelements necessary to combustion, or the greater part of these elementsat suitable spots and in suitable directions. The gaseous elementshaving previously been compressed and if desired heated, their mixtureis ignited and yields -a part of its heat to the molten mass.

After having passed through the molten mass, the gaseous combustionproducts travel upwardly through the vertical shaft and passthrough thefresh raw materials which are continuously introduced at the top anddrop freely in the shaft. These materials are preferably in the solidstate and in a more or less finely dividedcondition, and they areuniformly distributed over all the cross-section of the shaft by adispersion apparatus.

The degree of division of the raw materials and their specific weight onthe one hand, the upward rate of flow of the fumes on the other handdetermine the rate of fall of the particles and the duration of theircontact with the fumes before they reach the surface of the bath.Preferably conditions will be such that the preheated raw materials Willreach the bath at a temperature near the temperature of the burned gasesescaping therefrom.

The vertical shaft forining the upper portion of the oven may have avarying cross section at different levels so as to vary the upward speedof the fumes and, in correlation therewith, the downward speed of theraw materials. Thus we found an advantage in constricting the crosssection towards the bottom of the shaft and on the contrary, inenlarging it towards the fumes outlet.

The molten glass is Withdrawn from the melting pot through an openingnormally immersed in the bath. It may be desirable to reserve in the pota zone where the finished glass escapes the turbulence of the flame, sothat it can be subjected to some extent to refining. This zone of restmay be formed by an extension of the pot extending laterally or towardsthe bottom of the active portion.

The glass withdrawn may be used immediately for shaping operations, orit may be subjected to a supplementary refining operation in a furnaceof any known or suitable type operating in combination with the meltingoven.

The outlet for thecombus'ti'on products from the vertical shaft formingthe upper portion of the furnace may beconnected to one or more heatexchangers for preheating the fuel gas and/ or the combustion air, andsuch heat exchangers may be combined with a mechanical device such as agas turbine,"driven by the partially cooled expanding combustionproducts in order to supply all or part of the energy necessary forcompressing the fuel gas and/ or the combustion air.

The accompanying drawing, diagrammatically illustrates by way of examplean apparatus constructed in accordance with the present invention.

a is a shaft furnace at the bottom of which is a meltingpot b containingthe molten glass through whichpass flame jets. Theg'as es are blown athigh speed and pressure through nozzles c comprising'two concentricpipes, one for the combustion air, the other for the fuel.

After having yielded a part of the heat to the molten bath, the fumestravel in contra current to and heat the raw materials falling as aspray in the shaft a.

In the lower part of the furnace is a constriction d which has a doublefunction, On the one hand it reduces the radiation losses from thesurface of the molten bath, on the other hand it increases the rate offlow'of the fumes, so that the falling materials remain in suspensionabove the constriction d.

By momentarily decreasing the supply of the gases, a certain amount ofraw materials are caused to drop onto the surface of the bath. Periodicvariationsin'the supply of gases may be produced by providingin theinlet pipes of the furnace mechanically operated valves 1 and 2 adaptedto throttle, at predetermined intervals of time, the cross sectionalarea of the pipes. T he valves 1 and'2 shown in the drawing arecontrolled by a camv and have a valve member u. By this means, theduration of the contact of the raw material with the fumes, before theirintroduction into the bath, may be regulatedat will.

The raw materials are charged into a hopper a pro vided with a rotatingfeeder j which permits ofadmitting them into the furnace in spite of thehigher pressure therein. A Worm g carries the materialsinto the centralfeeding tube 12. As they leave this tube themate'rials are dispersedspray-fashion by a jet 'of air pressure blown from the tube i.

Above the constriction :1 the shaft flares upwardly, so that the rate offlow of the fumes decreases as they rise, and opposite the fumes outletit isso low that no part of the raw materials is carried towards therecupcra'tors.

As they come out of the shaft, the fumes enter a recuperator j in whichtheir pressure and rate of flow "are still sufiiciently great to ensurean'efiicient heat'exchange with the combustion air. They are thenexpanded in a gas turbine k which drives the air blower (n and gasblower I. On leaving the gas turbine the fumes pass through a secondrecuperator n and then are let out to the atmosphere through'o.

The combustion air compressed by the turbo-blower n'z successivelypasses through the recuperators n and j, and arrives at high temperaturein the air chamber for the nozzles c. A distributor with fluid-tightfeeding chamber .9 permits of introducing into the air pipe reagents inthe form of very fine powder.

The fuel gas compressed by the turbo-blower l is sent to the gaschamberfor the nozzles c.

The glass melted in the furnace passes under a Wall p into a refiningzone q Where occluded bubbles are allowed to escape; it is collected atr or directed towards shaping or other apparatus.

In order to start the plant, the gas is first ignited at the nozzles c,without air pressure being introduced. The flame burns freely in contactwith the air contained in the furnace. The necessary delivery ofcompressed air, then is gradually admitted. A certain quantity of brokenup glass is then charged, which quickly 'm'elts, whereupon the feedingof composition through It and its distribution by glass has been moreparticularly dealt with, the apparatus according to this invention isalso applicable to the fusion of like materials, such as those mentionedabove.

We claim:

1. An apparatus for melting glass and the like comprising, incombination, a shaft communicating at its bottom with a melting pot,said shaft having a constriction above said melting pot, nozzles openinginto the bottom of said pot for supplying air to said pot, and nozzlesopening into the bottom of said pot for supplying gas thereto, eachnozzle for supplying air adjoining a nozzle for supplying gas, wherebythe gas and the air inter-mix immediately upon leaving the respectivenozzles, means at the top of said shaft for supplying powdered rawmaterials into said shaft and for delivering said materials as a sprayover substantially the entire cross-sectional are of the shaft, and anoutlet above said last-named means for evacuating gases from said shaft.

2. An apparatus for melting glass and the like as de- References Citedin the file of this patent UNITED STATES PATENTS 351,413 Wainwright Oct.26, 1886 2,131,599 Shrum Sept. 27, 1938 v FOREIGN PATENTS 651,687Germany Oct. 18, 1937

1. AN APPARATUS FOR MELTING GLASS AND THE LIKE COMPRISING, INCOMBINATION, A SHAFT COMMUNICATING AT ITS BOTTOM WITH A MELTING POT,SAID SHAFT HAVING A CONSTRUCTION ABOVE SAID MELTING POT, NOZZLES OPENINGINTO THE BOTTOM OF SAID POT FOR SUPPLYING AIR TO SAID POT, AND NOZZLESOPENING INTO THE BOTTOM OF SAID POT SUPPLYING GAS THERETO, EACH NOZZLEFOR SUPPLYING AIR ADJOINING A NOZZLE FOR SUPPLYING GAS, WHEREBY THE GASAND THE AIR INTER-MIX IMMEDIATELY UPON LEAVING THE RESPECTIVE NOZZLES,MEANS AT THE TOP OF SAID SHAFT FOR SUPPLYING POWDERED RAW MATERIALS INTOSAID SHAFT AND FOR DELIVERING SAID MATERIALS AS A SPRAY OVERSUBSTANTIALLY THE ENTIRE CROSS-SECTIONAL ARE OF THE SHAFT, AND AN OUTLETABOVE SAID LAST-NAMED MEANS FOR EVACUATING GASES FROM SAID SHAFT.